Some of manufacture equipments now used in production processes are equipped with a fluid visual inspection device 10 on fluid visual inspection pipe for inspecting fluid flow condition. Referring to FIGS. 1 and 2, the conventional fluid visual inspection device 10 comprises a duct 11, a partition 12, an elastic element 13 and a fastening cap 14. The duct 11 has a transparent window 111 and houses a rotatable vane 112, and a threaded portion 113 at one end to couple with a fluid pipe and a flange 114 at another end formed at a smaller diameter with an external threaded portion 1141 formed thereon to be fastened to the fastening cap 14. The partition 12 has an aperture 121 and is held in the flange 114 with the elastic element 13 resting thereon. The fastening cap 14 has a first internal screw hole 141 at one end screwing with the external threaded portion 1141 of the flange 114 so that the fastening cap 14 compresses the duct 11 after screwing with the elastic element 13 butting one side of the partition 12. The fastening cap 14 has a second internal screw hole 142 at another end to couple with the fluid pipe. The pipe coupled with the fastening cap 14 is inlet side, while the one coupled with the duct 11 is outlet side. When fluid flows in through the fastening cap 14, it passes through the aperture 121 of the partition 12 and enters the duct 11 to drive the vane 112 to generate rotation, then flows out through the duct 11. Thus fluid flow condition can be determined.
Although the conventional fluid visual inspection device 10 mentioned above can be used to determine fluid flow condition, it usually is formed integrally with the duct 11. Fabrication and assembly are difficult and more costly, and require longer production time. Coupling of the fluid visual inspection device 10 and the fluid pipe also is more difficult.